The E710.2.3 cell line is a cloned murine CD4- CD8- thymic T lymphoma cell line, originally isolated from a thymic tumor of an AKR/J mouse. When cultured by itself at low density, E710.2.3 does not proliferate spontaneously, unless it is stimulated with phorbol 12-myristate 13-acetate (PMA). E710.2.3 can be stimulated to proliferate by contact with thymocytes or splenocytes. However, E710.2.3 can proliferate spontaneously when cultured at high density in the absence of PMA or other cells. When E710.2.3 is injected into syngeneic mice it grows as a malignant tumor in lymphoid organs and the thymus.